Reverse spot face tool

[thehomeengineer]

Hi All
Two casting I am currently working on (Trunk Guides for Foden steam wagon) need some spot faces so the nuts can clamp the casting up square and flat to the cylinder block. But it is impossible to use a standard counter bore or slot drill etc. So I decided to make two reverse spot face tools. One 3/8” and the other 1/4” diameter. The tools would be mounted to a pilot tool 3/16” and 1/8” diameter respectively. Yes these can be purchased but it isn’t a tool I could see myself using that often so decided to make them.

The counter bore was made from 10mm diameter silver steel and turned down to the correct diameter once the machining of the cutting edges were completed.

Initially the first counter bore I made didn’t work as I forgot the pilot need to drive the tool and I made the hole go all the way through. So the next was made with a flat bottom hole so once the top was machined the pilot tool would lock in place like a cam. The counter bore cutting edges were machined and then transferred to the tool and cutter grinder to put the cutting angle on each edge. Then turned to correct diameter as previously mentioned.

The counter bore cutter was then machined down on the mill to the flat bottom hole so it broke through and left 2mm high spigot to locate on the pilot shaft.

Both pilot shafts were machined from mild steel and the counter bore cutters were heat treated.

The photos below will hopefully help make this all a bit clearer.

One of the pilot shafts machined with a 2mm slot at 45 degrees.

Cutting edges machined.

Clearance angle ground on bottom edge.

Both counter bores ready for milling operation.

Heat treated ready to use

Test fit of tool in casting.

Casting clamped to drill table with reverse counter bore depth set with block.

As the cutter is working in the opposite direction the block fits under the stop.

First spot faces completed (3/8”diameter).

Casting in position on cylinder block.

This was the first one I a made and had to weld so I could lock to the pilot but hopefully shows how the cutter locks to the pilot shaft.

Thank you for taking the time to view
The Home Engineer